WASHINGTON (CNN) -- The Supreme Court agreed Monday to decide if the Navy is doing enough to protect whales from the effects of its sonar testing.

Environmentalists successfully sued the Pentagon over the practice in March, forcing major changes in the Navy's annual offshore training exercises.

A federal judge ruled it was "constitutionally suspect" for President Bush to issue a national security exemption so no environmental impact assessment was carried out.

One of the environmental organizations that sued the Defense Department said it had expected the Supreme Court decision and was ready to fight on.

"It's clear both that high intensity military sonar can injure and kill whales, dolphins, and other marine life and that the Navy can reduce the risk of this harm by commonsense safeguards without compromising our military readiness," said Joel Reynolds of the National Resources Defense Council.

"These have been the unanimous conclusions of every court that has considered this issue, even after President Bush in January sought unsuccessfully to intervene on the Navy's behalf," he said.

The Navy says the courts are protecting sea creatures rather than people. The Justice Department had asked the high court to revisit the federal appeals court ruling against the government.

The restrictions imposed by the court, said the Justice Department, could hamper military readiness in a time of war because sonar technology is used to detect increasingly sophisticated enemy submarines.

"In ordering additional mitigation to reduce the risk to marine mammals, the order shifts the risk to sailors and Marines," Navy spokesman Capt. Scott Gureck said in March.

The waters of southern California are home to dozens of species of whales, dolphins, seals and sea lions, nine of them endangered or threatened. Federal courts have cited scientific studies and the Navy's conclusions that high levels of sonar can cause hearing loss and disorientation in the animals.

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In February, the U.S. Navy demonstrated its on-board procedures for turning down sonar when whales come within 1,000 meters, and shutting it off completely when they approach 200 meters.

The sonar sounds like a "ping, ping" noise, and it can be reduced as necessary, officers said.

But environmentalists say the sonar can hurt whales farther than 1,000 meters away.

The appeals court cited studies that whales have stranded themselves and died kilometers away from sites where the Navy used sonar, said Joel Reynolds of the Natural Resources Defense Council.

It's "not just a question of a couple of hundred yards," he said.

The defense council, which filed the original lawsuit against the Navy to stop the Navy from conducting planned exercises, accuses the Bush administration of failing to conduct a thorough environmental impact study.

The federal National Oceanic and Atmospheric Administration had given the Navy permission to continue to train, citing measures put in place to minimize the impact on the mammals.

The issue now is whether the lower courts properly blocked the use of sonar in the military exercises after the White House cited an "emergency circumstance" that prevented an environmental impact statement from being issued.

In 2000, 16 whales beached themselves in the Bahamas after the Navy concluded too many sonar ships were operating in a narrow underwater channel. The service says it is providing $16 million for independent research to minimize sonar's effect on marine mammals.

In other developments:

• The court refused to intervene in a dispute over a controversial border fence being built along the U.S.-Mexican border, a victory for the Bush administration over enviromentalists and homeowners. Opponents had challenged a law giving the secretary of homeland security the power to bypass laws or regulations prohibiting the fence's construction.

• A criminal defendant has a constitutional right to a lawyer in some preliminary court proceedings, the court ruled in an 8-1 decision. The case involved Texas defendant Walter Rothgery, who was arrested in July 2002 on felony suspicion of having a gun. He was not appointed a lawyer until after the indictment six months later. Charges were later dropped.

• In a 7-2 decision, Justice Ruth Bader Ginsburg wrote for the majority, "Appellate courts may not reach out to correct a sentencing error when the government has not invited such error by appealing or cross-appealing." The case stemmed from an appeal in which a federal appeals court had ruled a lower court erred in making Michael Greenlaw's sentence so short. The appeals court said the sentencing jeopardized the court system's integrity.

• The court agreed to hear whether maternity leave should be counted in deciding pension eligibility. A 1979 federal law said companies had to treat such time off just like any disability. The question is whether women should have full credit if they gave birth before the law was enacted.

• The court also will hear whether the brother of a victim of alleged Iranian terrorism can collect $2.8 million based on an international tribunal decision. Dariush Elai's brother was killed in Paris, France, in 1990, and the French government blames Iran. The brother sued Iran in U.S. courts, and the U.S. government gave him money from frozen Iranian assets. The issue now is whether the brother can also collect from a defense contractor who owes Iran money from a canceled weapons contract.

• Justices agreed to hear whether a congressional law providing funds for poor capital defendants applies to state clemency efforts. The appeal stems from the case of Edward Harbison, who was convicted in 1983 of beating an elderly woman to death.

• For a third time, justices will hear the case of convicted Tennessee killer Gary Cone, who claims prosecutors concealed evidence that may have helped him avoid the death sentence. Cone admits the killing, but says he was a troubled Vietnam veteran high on drugs when he committed it.